The proposed study will evaluate the reliability and validity of a calibrated self-report instrument called the Youth Activity Profile (YAP) for assessig youth physical activity (PA) and sedentary behavior (SB). Considerable work has been done to improve objective monitoring techniques but the systematic use of calibration procedures provides a way to improve the utility of self- report instruments for research and public health surveillance. With appropriate calibration, it is possible to convert self-reported PA and SB data into estimates that correspond to more accurate values obtained using objective measures. This would make it possible to obtain accurate, group level estimates of PA and SB using less expensive feasible methods. Preliminary calibration of the YAP demonstrates that it can produce accurate group estimates of PA and predict compliance with established public health guidelines for PA. The proposed study will build on this work by calibrating and evaluating web-based versions of the YAP that will enable broader adoption in school based programming and youth research. The 3 independent aims will allow us to continue our systematic refinements of this promising public health tool. In Aim 1 we will determine the reliability and equivalence of th three different versions of the YAP (Print, Online, and Online Game). We will administer the 3 different versions to intact classrooms from 12 different schools (36 classrooms total) on two occasions (1-2 weeks apart) to examine the test-retest reliability and equivalence of the alternative formats. In Aim 2 we will develop and test new calibration algorithms for use with the web-based versions of the YAP. Data will be collected with the online version (using our established protocol) in two regionally distinct metropolitan school systems (Des Moines and Dallas) across a full academic school year to increase the generalizability of the algorithms. In Aim 3 we will test the validity and equivalence of the web-based versions of the YAP through a large participatory research network involving over 1000 schools (NFL PLAY 60 FITNESSGRAM(R) Partnership Project). Construct validity will be evaluated for both the Online and Online Game versions by examining correlations with group level estimates of physical fitness from the FITNESSGRAM battery. Age and gender patterns of PA from the Online and Online Game versions will be evaluated for equivalence and, if necessary, output from the Game version will be standardized using a test- equating step. The proposed study will systematically evaluate the utility of the web-based formats of the YAP for school-based research on PA and SB. With additional refinement, these tools can facilitate the systematic evaluation of youth PA and SB patterns across the country.